/*
 * Copyright (C) 2009 The JSR-330 Expert Group
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package jakarta.inject;

import static java.lang.annotation.ElementType.ANNOTATION_TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

/**
 * Identifies scope annotations. A scope annotation applies to a class containing an injectable
 * constructor and governs how the injector reuses instances of the type. By default, if no scope
 * annotation is present, the injector creates an instance (by injecting the type's constructor),
 * uses the instance for one injection, and then forgets it. If a scope annotation is present, the
 * injector may retain the instance for possible reuse in a later injection. If multiple threads can
 * access a scoped instance, its implementation should be thread safe. The implementation of the
 * scope itself is left up to the injector.
 *
 * <p>In the following example, the scope annotation {@code @Singleton} ensures that we only have
 * one Log instance:
 *
 * <pre>
 *   &#064;Singleton
 *   class Log {
 *     void log(String message) { ... }
 *   }</pre>
 *
 * <p>The injector generates an error if it encounters more than one scope annotation on the same
 * class or a scope annotation it doesn't support.
 *
 * <p>A scope annotation:
 *
 * <ul>
 *   <li>is annotated with {@code @Scope}, {@code @Retention(RUNTIME)}, and typically
 *       {@code @Documented}.
 *   <li>should not have attributes.
 *   <li>is typically not {@code @Inherited}, so scoping is orthogonal to implementation
 *       inheritance.
 *   <li>may have restricted usage if annotated with {@code @Target}. While this specification
 *       covers applying scopes to classes only, some injector configurations might use scope
 *       annotations in other places (on factory method results for example).
 * </ul>
 *
 * <p>For example:
 *
 * <pre>
 *   &#064;java.lang.annotation.Documented
 *   &#064;java.lang.annotation.Retention(RUNTIME)
 *   &#064;jakarta.inject.Scope
 *   public @interface RequestScoped {}</pre>
 *
 * <p>Annotating scope annotations with {@code @Scope} helps the injector detect the case where a
 * programmer used the scope annotation on a class but forgot to configure the scope in the
 * injector. A conservative injector would generate an error rather than not apply a scope.
 *
 * @see jakarta.inject.Singleton @Singleton
 */
@Target(ANNOTATION_TYPE)
@Retention(RUNTIME)
@Documented
public @interface Scope {}
